The present invention relates to a susceptor set in a process chamber and capable of bearing an object to be processed thereon, and more particularly, to a susceptor capable of preventing the object from being dislocated as the pressure in the process chamber varies.
Semiconductor manufacturing processes include a film-forming process, in which W (tungsten), WSi (tungsten silicide), Ti (titanium), TiN (titanium nitride), TiSi (titanium silicide) or some other metal or metallic compound is deposited on a semiconductor wafer (hereinafter referred to as "wafer") as an object to be processed by the CVD method, in order to form a wiring pattern on the wafer or fill up recesses between wires.
A process apparatus for carrying out this film-forming process is provided with a process chamber and a susceptor therein. The susceptor is formed of a thin carbon material or ceramics. Halogen lamps or the like for heating the wafer through a permeable window of quartz are arranged under the susceptor. The susceptor is facing by a showerhead, which feeds WF.sub.6, SiH.sub.4, etc. as process gases into the process chamber in order to form a metallic film of W or WSi on a wafer. Further, the process apparatus is provided with an exhaust system, which is connected to an exhaust port of the process chamber. The exhaust system serves to decompress the process chamber by suction, thereby setting the interior of the chamber at a given degree of vacuum, e.g., 1 Torr to 80 Torr.
In the film-forming process using the process apparatus of this type, the wafer is fixedly positioned on the susceptor as its peripheral edge portion is pressed against the susceptor by means of a clamp ring. If the metallic film is formed on the wafer with the peripheral edge portion of the wafer pressed by the clamp ring, however, the wafer edge portion inevitably involves areas that remain unaffected by any film.
To cope with this, there is a method in which film formation is achieved by placing the wafer in a depressed section that is provided in the susceptor, instead of fixing the wafer by means of the clamp ring. According to this method, the process chamber is evacuated and decompressed with the wafer simply placed in the depressed section. The wafer is heated indirectly by means of halogen lamps or the like as WF.sub.6, SiH.sub.4, etc. are supplied from a showerhead, and a metallic film of W or WSi is formed on the wafer. If the wafer is subjected to the film-forming process or the like in a manner such that it is simply placed on the susceptor without being fixed thereto, as in this method, however, it may possibly slightly move on the susceptor when the pressure in the process chamber is changed. If the pressure in the process chamber is lowered, for example, from several Torr or more to 1 Torr or less by means of a vacuum pump, the wafer may be dislocated by, for example, 1 to 2 mm, in some cases. Possibly, such dislocation may result in errors in wafer transportation.